crypto: af_alg - Fix race around ctx->rcvused by making it atomic_t

This variable was increased and decreased without any protection.
Result was an occasional misscount and negative wrap around resulting
in false resource allocation failures.

Fixes: 7d2c3f54e6f6 ("crypto: af_alg - remove locking in async callback")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/af_alg.c

@@ -664,7 +664,7 @@ void af_alg_free_areq_sgls(struct af_alg_async_req *areq)
 	unsigned int i;
 
 	list_for_each_entry_safe(rsgl, tmp, &areq->rsgl_list, list) {
-		ctx->rcvused -= rsgl->sg_num_bytes;
+		atomic_sub(rsgl->sg_num_bytes, &ctx->rcvused);
 		af_alg_free_sg(&rsgl->sgl);
 		list_del(&rsgl->list);
 		if (rsgl != &areq->first_rsgl)
@@ -1162,7 +1162,7 @@ int af_alg_get_rsgl(struct sock *sk, struct msghdr *msg, int flags,
 
 		areq->last_rsgl = rsgl;
 		len += err;
-		ctx->rcvused += err;
+		atomic_add(err, &ctx->rcvused);
 		rsgl->sg_num_bytes = err;
 		iov_iter_advance(&msg->msg_iter, err);
 	}

crypto/algif_aead.c

@@ -571,7 +571,7 @@ static int aead_accept_parent_nokey(void *private, struct sock *sk)
 	INIT_LIST_HEAD(&ctx->tsgl_list);
 	ctx->len = len;
 	ctx->used = 0;
-	ctx->rcvused = 0;
+	atomic_set(&ctx->rcvused, 0);
 	ctx->more = 0;
 	ctx->merge = 0;
 	ctx->enc = 0;

crypto/algif_skcipher.c

@@ -390,7 +390,7 @@ static int skcipher_accept_parent_nokey(void *private, struct sock *sk)
 	INIT_LIST_HEAD(&ctx->tsgl_list);
 	ctx->len = len;
 	ctx->used = 0;
-	ctx->rcvused = 0;
+	atomic_set(&ctx->rcvused, 0);
 	ctx->more = 0;
 	ctx->merge = 0;
 	ctx->enc = 0;

include/crypto/if_alg.h

@@ -18,6 +18,7 @@
 #include <linux/if_alg.h>
 #include <linux/scatterlist.h>
 #include <linux/types.h>
+#include <linux/atomic.h>
 #include <net/sock.h>
 
 #include <crypto/aead.h>
@@ -150,7 +151,7 @@ struct af_alg_ctx {
 	struct crypto_wait wait;
 
 	size_t used;
-	size_t rcvused;
+	atomic_t rcvused;
 
 	bool more;
 	bool merge;
@@ -215,7 +216,7 @@ static inline int af_alg_rcvbuf(struct sock *sk)
 	struct af_alg_ctx *ctx = ask->private;
 
 	return max_t(int, max_t(int, sk->sk_rcvbuf & PAGE_MASK, PAGE_SIZE) -
-			  ctx->rcvused, 0);
+		     atomic_read(&ctx->rcvused), 0);
 }
 
 /**